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Re: Alxasaurus and segnosaurs



On Tue, 6 Feb 1996, Jeffrey Martz wrote:

> 
> > >      Is is remotely possible the segnosaurs are paraphyletic?
> > 
> >     I think that this would SUCK! Or as people say from Seattle LAME!
> >     IMHO, I think you mean Polyphyletic?
> 
>     I mean some being theropods and others being sauropodomorphs, or some 
> being sauropodomorphs and others being ornithischins or whatever, and 
> there just being a lot of covergence.    
> 

That is, indeed, polyphyly.  "Paraphyletic" refers to a (usually 
unspecialized) basal assemblage whose (usually specialized) descendants are 
classed outside the group, while "polyphyletic" 
refers to unrelated groups being classed together.  

For example, the "family Pongidae," supposed to include orang-utans, 
chimpanzees, and gorillas, but not humans, is paraphyletic (these animals 
are indeed descended from a common ancestor, but there is another animal, 
the human being, that is also descended from this common ancestor but is 
not included in the taxon).

The "Pachydermata," on the other hand, was a taxon conceived to hold 
tapirs, horses, rhinos, elephants, and hippos.  This assemblage is 
polyphyletic, the features supposedly uniting this group having appeared 
independently in each lineage.


> LN Jeff
> 

Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447
(206)535-8204
PharriNJ@PLU.edu

"If you can't convince them, confuse them." -- Harry S. Truman